It is well known that the presence of nitrogen and poly-nuclear aromatics (“PNA’) in heavy oil fraction feedstocks have a detrimental effect on the performance of the hydrocracking unit. For example, in the operation of one refinery where the hydrocracker was fed by a de-metalized or de-asphalted stream included a high level of impurities such as nitrogen-containing compounds and PNA coming from a solvent de-asphalting unit were found to be present at 5-10% of the volume of the feedstock stream. The smoke point of kerosene product from the hydrocracking unit was less than 20 and the cetane number of diesel product from the hydrocracking was about 65. This compares unfavorably to a kerosene smoke point of at least 25 and a diesel cetane number of at least 70 from a hydrocracker running on a straight run vacuum gas oil or standard feedstock.
As used herein, a “standard feedstock” means one that has a very low volume and weight percent of nitrogen-containing and PNA compounds as measured by Micro Carbon Residue (MCR) and C5-asphalthenes. The MCR value is determined by ASTM Method Number D-4530. The C5-Asphalthenes value is defined as the amount of asphaltenes precipitated by addition of n-pentane to the feedstock as outlined in the Institute of Petroleum Method IP-143. A standard feedstock preferably has not more than 1000 ppmw of nitrogen and less than 1 W % of MCR or less than 500 ppmw of C5-Asphalthenes.
Various processes have been proposed for removal of compounds that reduce the efficiency of the hydrocracking unit and/or the quality of the products produced. For example, a two-stage process for the removal of polycyclic aromatics from hydrocarbon feedstreams in disclosed in U.S. Pat. No. 4,775,460. The first stage includes contacting the feedstream with a metal-free alumina to form polycyclic compounds or their precursors; this is followed by a second stage for removing the polycyclic compounds by contacting the feed with a bed of adsorbent, such as charcoal. These process steps are conducted at elevated temperatures, relatively low pressure, and preferably in the absence of hydrogen to avoid any hydrocracking of the heavy feedstream.
A process is disclosed in U.S. Pat. No. 5,190,633 for the separation and removal of stable polycyclic aromatic dimers from the effluent stream of the hydrocracking reactor that employs an adsorption zone, suitable adsorbents being identified as molecular sieves, silica gel, activated carbon, activated alumina, silica-alumina gel and clays. The adsorbent is preferably installed in a fixed-bed, in one or more vessels, and either in series or parallel flow; the spent zone of adsorbent can be regenerated. The heavy hydrocarbon oil passing through the adsorption zone is then recycled to the hydrocracking zone for further processing and conversion of lower boiling hydrocarbons.
In a refinery, the hydrocracking feedstock can be a blend of vacuum gas oil (“VGO”) and de-metalized oil (“DMO”) or De-Asphalted oil (“DAO”) that is supplied by the n-paraffin de-asphalting units (where n-paraffin can include propane, butane, pentane, hexane or heptane) such as a DEMEX™ Process (a de-metallization process licensed by UOP). Processes for separating a resin phase from a solution containing a solvent, de-metallized oil and a resin are described in U.S. Pat. Nos. 5,098,994 and 5,145,574. A typical hydrocracking unit processes vacuum gas oils that contain from 10-25 V % of DMO or DAO in a VGO blend for optimum operation. It has been found that the DMO or DAO stream contains significantly more nitrogen compounds (2,000 ppmw vs. 1,000 ppmw) and a higher MCR content than the VGO stream (10 W % vs. <1 W %).
The DMO or DAO in the blended feedstock to the hydrocracking unit can have the effect of lowering the overall efficiency of the unit, i.e., by causing higher operating temperature or reactor/catalyst volume requirements for existing units or higher hydrogen partial pressure requirements or additional reactor/catalyst volume for the grass-roots units. These impurities can also reduce the quality of the desired intermediate hydrocarbon products in the hydrocracking effluent. When DMO or DAO are processed in a hydrocracker, further processing of hydrocracking reactor effluents may be required to meet the refinery fuel specifications, depending upon the refinery configuration. When the hydrocracking unit is operating in its desired mode, that is to say, producing products in good quality, its effluent can be utilized in blending and to produce gasoline, kerosene and diesel fuel to meet established fuel specifications.
It is therefore a principal object of the present invention to provide a process for improving the petroleum or other sources including shale oil, bitumen, tar sands, and coal oil feedstock to a hydrocracking unit or to a fluid catalytic cracking unit by removing high-nitrogen containing compounds and poly-nuclear aromatic hydrocarbons that deactivate active on the hydrocracker catalyst or fluid catalytic cracking catalysts.
It is another object of the invention to improve the quality of the feedstock derived from petroleum, shale oil, bitumen, tar sands and coal oils to a hydrocracking or fluid catalytic cracking unit in order to improve the overall efficiency of the hydrocracking or fluid catalytic cracking process, and the yields and quality of the products produced.
Another object of the invention is to increase the hydrocracking unit processing capacity for processing heavier feedstock materials such as DMO or DAO or VGO or heavy cycle oils from a fluid catalytic cracking unit (HCO), visbroken oil (VBO), coker gas oils (CGO) alone or in blends with vacuum gas oils without modifying the structure of the existing hydrocracking unit.
Yet another object of the invention is to provide a hydrocracking process improvement that will have a positive effect on catalyst activity and stability, to increase the useful life of the catalyst, and to thereby reduce operating costs.
It is yet another object of the invention to increase the fluid catalytic cracking conversion rate, i.e., to increase the yield of gasoline while minimizing the production of undesirable side products such as coke and total C1-C2 gas yields.
It is another object of the invention to decrease catalyst consumption in fluid catalytic cracking process unit operations by providing a feedstock which nitrogen containing compounds and poly-nuclear aromatic compounds have been removed.
It is another object of the invention to reduce the emissions of oxides of sulfur and nitrogen (SOX and NOX) in fluid catalytic cracking process unit operations.